Combustion system comprising sponge metal, liquid oxygen, and finely divided carbon



United States Patent 3,259,532 COMBUSTION SYSTEM COMPRISING SPONGE METAL, LIQUID OXYGEN, AND FINELY DIVIDED CARBON William Gray Reynolds, Richmond, Va., assignor to Reynolds Metals Company, Richmond, Va., :1 corporation of Delaware No Drawing. Filed July 24, 1963, Ser. No. 297,207 2 Claims. (Cl. 149-1) This invention relates to a combustion system comprising a combustible sponge metal and liquefied oxygen. More particularly the invention concerns a novel explosive, propellant, and blasting composition including sponge aluminum, a liquefied oxygen containing gas, and a carbonaceous material.

The combustibility of aluminum metal has for a long time attracted investigators seeking to utilize this property in explosive and blasting compositions. In US. Patent 1,375,243 there is disclosed an explosive composition including a metal powder such as aluminum or magnesium mixed with a combustible absorbent material such as sawdust, cotton or coal, to which liquid air is added. This composition does not appear to have found practical application, possibly because of problems of instability and difiiculty of control of its action. More recently, aluminum powders and granules have been in-- corporated in solid propellants, but these are intended for specialized uses such as rocket fuels. Moreover in the latter types of compositions, the oxygen is present in chemically combined form, rather than in the free state.

Blasting preparations for use in mining and tunneling are known, in which combustible materials such as charcoal, carbon black, sawdust, or wood pulp, in a loose porous mass, are formed into cartridges in a proper wrapping, and soaked in liquid oxygen immediately prior to use. They are then placed in a bore hole, and after tamping, are fired directly or by fuse. This type of explosive has the disadvantage of exceedingly short life owing to evaporation of the oxygen. The contents of the cartridge become embrittled upon exposure to liquid oxygen and generally cannot be impregnated a second time for reuse.

In accordance with the present invention, there is pro vided a novel combustion system whereby the advantages of combustible metal fuel are combined with those of liquid oxygen in a unique manner to form an explosive, propellant, or blasting composition which possesses properties of safety, reliability and ease of control. The composition of the invention includes as an essential element thereof a metal sponge of a combustible metal such as aluminum or magnesium. By the term metal sponge is meant a rigid metal matrix which contains distributed throughout its inner portion, in a generally uniform manner, a multiplicity of discrete interconnecting cells or pores, which communicate with each other. This material is to be differentiated from metal foams in which the pores or cells are closed and do not interconnect or communicate. Such metal sponge is known and is employed, for example in porous filters and porous metal bearings. The interconnected cells allow free passage of liquid or gas, as well as the sifting into the interstices of the metal sponge, of finely divided solid materials.

In the composition of the invention, the metal sponge has incorporated in the interstices thereof, liquid oxygen. In accordance with another form of the invention, the

liquid oxygen is admixed with a finely divided combustible material such as a carbonaceous substance, for example, finely divided carbon, which is dispersed in the liquid oxygen and the mixture is incorporated or infiltrated into the interstices of the metal sponge.

The sponge aluminum or magnesium elements can be prepared in accordance with known methods, such as, for example, molding a bat-ch of metal particles or powder in a suitably shaped lubricated die under a pressure of about 10,000 pounds per square inch, there being added to the metal powder a suitable pore forming agent such as ammonium bicarbonate, followed by sintering for several hours at a temperature of about 500 C., to yield a rigid metal sponge about porous, and having a rod shape.

The sponge metal rods are dipped in liquid oxygen and the latter is allowed to penetrate to saturation. The amount absorbed may range from about 40 to 50 percent by weight of the final product, depending upon the size and distribution of the pores and the ratio of voids to metal. Alternatively, the sponge metal rod may be clipped in a suspension of carbon black in liquid oxygen for a period of time suflicient for the mixture to penetrate the interstices of the sponge. The amount of carbon is important, and may range from about 20 to 30 percent by weight of the final product. In order to aid in retention of the saturant, the metal sponge rod may be encased in a suitable casing, such as a cardboard or thin metal foil or tube, which may be sealed at one end.

The invention is illustrated by the following example, which is not to be regarded as limiting:

Example A rod of aluminum sponge is prepared having the dimensions, one inch in diameter and one foot in length. It is wrapped in aluminum foil so as to enclose one end and the circumference. A suspension of channel black is made in liquid oxygen, the amount of channel black being 20 percent by weight of the final product, and the suspension is poured into the open end of the sponge rod until no more is absorbed. The sponge rod may also be filled by submerging in liquid oxygen, and prior evacuation may be employed to aid filling. The rod is sealed with aluminum foil and maintained at liquid oxygen temperature prior to insertion into a bore hole in rock, and then detonated electrically. The rock shatters evenly and with little smoke, considerable heat being developed. The explosive rod as prepared is characterized by dimensional stability and light weight.

What is claimed is:

1. A combustion system comprising a rigid metal sponge of a combustible metal selected from the group consisting of aluminum and magnesium containing distributed throughout its interior a multiplicity of discrete interconnecting cells, said sponge having incorporated in the interstices thereof liquefied oxygen and a finely divided carbonaceous material dispersed in said liquefied oxygen, the amount of said carbonaceous material being from about 20% to about 30% by weight of the total weight of sponge metal, oxygen, and carbonaceous material.

2. A combustion system comprising aluminum metal sponge having distributed throughout its interior a multiplicity of discrete interconnecting cells, said sponge having incorporated in the interstices thereof liquefied oxygen and finely divided carbon dispersed in said lique- 3 4 fied oxygen, the amount of carbon being from about 20 OTHER REFERENCES percent to about 30 percent by weight of the total weight" Journal f Chemical EduC-afion, VOL 3 2 b of aluminum sponge, oxygen, and carbon. wary 1959, 5457,

References Cited by the Examiner 5 LEON D, ROSDOAL, Primary Examiner.

UNITED STATES PATENTS BENJAMIN R. PADGETI, CARL D. QUARFORTH, 1,397,826 11/1921 Weber n1 149-1 3,111,439 11/1963 Brunauer 149-1 A. G. BOWEN, Assistant Examiner. 

1. A COMBUSTION SYSTEM COMPRISING A RIGID METAL SPONGE OF A COMBUSTIBLE METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND MAGNESIUM CONTAINING DISTRIBUTED THROUGHOUT ITS INTERIOR A MULTIPLICITY OF DISCRETE INTERCONNECTING CELLS, SAID SPONGE HAVING INCORPORATED IN THE INTERSTICES THEREOF LIQUEFIED OXYGEN AND A FINELY DIVIDED CARBONACEOUS MATERIAL DISPERSED IN SAID LIQUEFIED OXYGEN, THE AMOUNT OF SAID CARBONACEOUS MATERIAL BEING FROM ABOUT 20% TO ABOUT 30% BY WEIGHT OF THE TOTAL WEIGHT OF SPONGE METAL, OXYGEN, AND CARBONACEOUS MATERIAL. 